For many years, bisexuals were left out of both heterosexual and homosexual society. Being neither lesbian/gay or straight, they had no symbols of their own for pride in being who they are. So, the overlapping triangles were created as a symbol of pride in being bisexual. This is (as far as I know) the most commonly used and accepted bisexual pride symbol. It should be noted that there have been many other variations on the use of a triangle as a pride symbol. Some of the variations include the rainbow triangle and the lavender triangle. Other triangles show pride in being lgbt AND being of a particular race or culture.